1. Field of the Invention
The present invention relates to a light quantity adjusting device suitable for use in an image taking apparatus such as a digital still camera.
2. Related Background Art
FIG. 6 shows a configuration of a shutter apparatus provided in a conventional lens shutter camera. In FIG. 6, reference numeral 101 denotes a permanent magnet, reference numeral 102 denotes a driver lever, and reference symbol 102a denotes a driver pin that is provided in the driver lever 102. The driver lever 102 is fixed to the permanent magnet 101, and rotates integrally with the permanent magnet 101. Reference numeral 103 denotes a coil, reference numerals 104 and 105 denote stators that are made from a soft magnetic material and are excited by a coil 103. The stator 104 and the stator 105 are joined together at portions denoted by 104a and 105a, and are regarded as integrated from the perspective of a magnetic circuit. The stator 104 and the stator 105 are excited, and the permanent magnet 101 is rotationally driven within a predetermined angle range by energization of the coil 103. Reference numerals 106 and 107 denote shutter blades, and reference numeral 108 denotes a base plate. The shutter blades 106 and 107 are rotatably attached to pins 108a and 108b of the base plate 108 via hole portions 106a and 107a, respectively. Slots (narrow hole) 106b and 107b are slidably fitted onto the driver pin 102a. By rotating the driver lever 102 together with the permanent magnet 101, the shutter blades 106 and 107 are rotatably driven about the hole portions 106a and 107a as centers, and an opening. (not shown) opens and closes.
Other configurations include forming the permanent magnet by using a plastic magnet, and forming the permanent magnet integrally with the driver pin, in order to prevent increases in cost.
Reference numeral 109 denotes a front base plate that movably holds the shutter blades 106 and 107 between the front base plate 109 and the base plate 108. Reference numeral 110 denotes a rear base plate that rotatably holds the permanent magnet 101.
Incidentally, digital cameras have been spreading. The digital cameras use an image pickup element such as a CCD to photoelectricaly convert a subject to be photographed into still image information. The subject to be photographed is then recorded onto a recording medium. Operations relating to light exposure in this type of digital camera are explained below in brief.
First, a main power source is turned on before photography. When the image pickup element is placed in an operating state, the shutter blades are held in an open position at which it is possible to expose light to the image pickup element. Electric charge accumulation and emission transfer are thus repeated by the image pickup element, and observation of the field of view via an image monitor becomes possible. Next, a stop value and an exposure time amount are determined according to output from the image pickup element at the point when a shutter release button is pressed. For cases where it is necessary to close the aperture of an exposure opening based on the stop value and the exposure time amount, first the aperture blades are driven and a predetermined aperture value is set. Next, an instruction is given to the image pickup element, from which accumulated electric charge is being released, to start accumulating electric charge. An accumulation start signal used for the instruction also acts as a triggering signal to activate an exposure time control circuit at the same time. After passing through a predetermined amount of exposure time, the shutter blades are driven to a closed position at which light exposure to the image pickup element is blocked. Transfer of the electric charge that has accumulated in the image pickup element is performed after the light exposure to the image pickup is blocked. Image information is recorded in a recording medium through an image writing device. Prevention of light exposure to the image pickup element is performed during charge transfer in order to prevent the electric charge from changing due to excess light during the charge transfer.
In addition to shutter devices like that described above, there are also devices that possess a mechanism for preventing movement of an ND filter, and devices that possess a mechanism for preventing movement of an aperture regulating member having a small aperture size.
It is difficult to fabricate the shutter devices described above into thin, compact devices because of the height of the coil and that of the stator (axial direction dimension).
Further, a motor device of a camera is disclosed in Japanese Patent Application Laid-Open No. 2000-324787. However, multiple parts overlap in a rotation axis direction, such as a base plate that is fixed to a rotor and a cover plate, and therefore it is difficult to form parts existing in the axial direction into a thin configuration.
Furthermore, in Japanese Patent Application Laid-Open No. 2002-51524, a driver device is configured by overlapping a coil, a stator, and the like to make the thickness of a radial direction of a driver device small. Therefore, it is difficult to make the axial direction thin.
Still further, Japanese Patent Application Laid-Open No. 2002-51526 discloses a device in which a sliding surface is provided in a stator in order to maintain a gap between a magnet and stators that sandwich the magnet.
The devices described above thus show that it is difficult to configure a thin device in its axial direction. However, a device disclosed in Japanese Patent Application Laid-Open No. 2002-49076 by the applicants of the present invention can be given as a light quantity adjusting device whose axial direction has been made thin.
A configuration of the light quantity adjusting device disclosed in Japanese Patent Application Laid-Open No. 2002-49076 is thin in the axial direction, which is described below.
The light quantity adjusting device has a driver device, a base plate provided with an opening portion, and a light quantity controlling member. The driver device has a stator having a first stator and a second stator. The stators are provided with magnets. The magnets have surfaces in a direction perpendicular to a virtual axis of a center of rotation divided in an angular direction with respect to the virtual axis so as to be alternately magnetized in different polarities, and are rotatable about the center of rotation. A coil is disposed in an outer circumference or an inner circumference of the magnet. The first stator and the second stator oppose an upper surface, a lower surface, and an inner circumferential surface of the magnet, and are excited by the coil. The driver device also has a driver pin structured integrally with the magnet. The light quantity controlling member regulates an opening amount of the opening portion of the base plate, and is driven by the driver pin of the driver device.
By using a light quantity adjusting device having this type of configuration, it becomes possible to make a device that is relatively thin and compact compared to conventional devices.